Re #8108. Add a test that the instrument is read in correctly.

This is for a nexus file that contains the full instrument XML.
Right now, it's still reading the external IDF - this test will make
sure things still work after the refactoring.
Re #8108. Generalise where to look for instrument.

Remove the hard-coding pointing to the ISIS place in favour of the
variable that's used everywhere else.
Re #8108. Use the LoadEventNexus loadInstrument static method.

As well as reducing code duplication, this method tries to load the
instrument from the nexus file if possible.
Re #8108. Refactor to correctly load from SNS ADARA files.

While also continuing to work for the other files that have the
instrument XML inside the nexus file (processed, ISIS files).
Re #8108. Add .nxs.h5 to list of file extensions.

Also fix some formatting.
Re #8108. Add loading of the parameter file to LoadIDFFromNexus.

However, the algorithm doesn't fail if the parameter file is missing.
Re #8108. Fix and enable the last test.

As far as I can tell, setting the filename at this point in
ExperimentInfo is not necessary.
Re #8108. Throw if unable to load instrument from IDF

Previously, this failure would just log and the calling algorithm
thought it had succeeded when it hadn't.
Re #8108. Remove redundant code.

The strings will be empty on construction anyway.
Re #8108. Check early for presence of IDF in nexus file.

It seemed rather heavyweight to launch and plough through most of
LoadIDFFromNexus & ExperimentInfo::loadNexus when the thing we want
isn't there anyway.
Re #8108. Add a magic line to tie logfile params to components.
Re #8108. Fix cut-and-paste mistake.
Merge remote-tracking branch 'origin/feature/8108_load_inst_from_adara_nexus_files'